The large® slab has also been rough cut (50 grit diamond pad). All samples have dried substantially lighter than expected. Not as hard to cut as expected after 4 weeks of curing. Next - slurry!


“Bystanders will need to consult drycleaners” was the motto on Monday night as the wet polisher was fired up for a “green” cut of the freshly de-molded castings. The concrete is amazingly tenacious when trying to release it from the molds. There were some small voids (to be expected - slurry is used to fix these) so a little more vibration would be useful next time around. The 50g of oxide (~0.5% by weight) gave a very dark grey mix. The 50 grit diamond pad made light work of exposing the aggregate / embedded items.


Today we brought down the rest of the gear and got ready for a test pour.

A couple more test molds were made - this time thinner 300 x 300 x 40 frames as well as some “egg ring” 90mm storm pipe circles for doing multiple small batch tests.

A special thanks to the team at Sika Australia who were good enough to donate 2L of Sika® ViscoCrete® PC HRF-2 High Range Water Reducer Retarder (say that quickly 3 times). This special concrete admix gives us a superplastic cement with low water (which means high strength) and quick demolding (for fast fabrication). Normally it comes in 20L minimum quantites which would be enough to make a couple of tons of concrete…

It was amazing how little water was needed to hydrate 15kg of mix (« 2L)!

First batch used grey cement, river sand, small black river stone and black oxide for a deeper grey mix. The fibres look quiet odd (like there's dog hair in the mix) - we shall see how they look in the final product. Samples included copper wire fragments, brass fasteners and other aggregates.

De-molding is set for Monday night with a “green” concrete cutting to expose the aggregate.

A thanks to jmuirhead for helping with the day's events…


OK so some test 300 x 300 x 50 forms have been built.

I'm currently building some 300mm diameter circular forms out of thin luan plywood as an experiment.

Standby for a pour very soon…


This is a placeholder for factotum's concrete benchtop project page.

The plan is to start with some trial 400 x 400 square forms fabricated from melamine.

Currently we have melamine, cement, oxide, aggregate, sand, poly fibres, mesh and a concrete vibrator.

What we'd really like at some point is a cement mixer for bigger pours.

And a new concrete polisher is on order…

  • projects/concrete.txt
  • Last modified: 2020/03/12 12:49
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